Composition for use in a magnetically fluidized bed

ABSTRACT

Novel compositions, and process for the operation of a magnetically stabilized fluidized bed. The compositions are characterized as a particulate material which can be oriented within, and formed into a magnetically stabilized fluidized bed which comprises: 
     (i) particles of average size ranging from about 10 micrometers (μm) to about 4000 μm, preferably from about 50 μm to about 500 μm, each containing a nonferromagnetic component, or components, and preferably a catalytically active component, or components, composited with a single elongated ferromagnetic component, the ferromagnetic component being multidomain, having dimensions of at least 1 μm in all directions and a length:diameter (L/D) ratio of at least 2 but not more than 17.3, said ferromagnetic component being present in the composite particles as an inclusion within a nonferromagnetic matrix constituting at least 0.5%, preferably at least 5%, but not more than 3/2(L/D) 2  of the total volume of each particle, where the L/D ratio is the ratio of the longest dimension of the ferromagnetic inclusion relative to the shortest dimension, and the particles can, in said magnetically stabilized fluidized bed rotate, or turn to line up the long dimensions of the ferromagnetic components parallel to the direction of the field and a short dimension perpendicular to the direction of the field; or 
     (ii) particles of average size ranging from about 10 micrometers (μm) to about 4000 μm, preferably from about 50 μm to about 500 μm, each containing a nonferromagnetic component, or components, and preferably a catalytically active component, or components, and within each of which is composited a plurality of elongated ferromagnetic components, the ferromagnetic component being multidomain, having dimensions of at least 1 μm in all directions, elongated in one or two dimensions, and having a length:diameter (L/D) ratio of at least 2 but not more than 313, preferably not more than 30, said ferromagnetic component being present in the composite particles as inclusions within a nonferromagnetic matrix, and oriented in such a way that there is a preferred direction in each particle such that all the ferromagnetic inclusions in that particle have a long dimension essentially parallel with said preferred direction and constituting at least 0.5%, preferably at least 5%, but for particles elongated in one dimension not more than 2π/3(L/D+1) 2 , and for particles elongated in two dimensions not more than π/2(L/D+1), of the total volume of each particle, where L/D is the average ratio of the longest dimension of ferromagnetic inclusion relative to the shortest dimension, and, in said magnetically stabilized fluidized bed, the particles can rotate, or turn to line up said preferred direction parallel to the direction of the field such that essentially all of the ferromagnetic inclusions have a long dimension essentially parallel to the direction of the field; and a fluid-solids contacting process wherein the composite particles characterized in (i) and (ii), supra, are formed into a magnetically stabilized fluidized bed.

BACKGROUND OF THE INVENTION AND PRIOR ART

This is a Continuation-in-part of application Ser. No. 943,552 filedSept. 18, 1978, now abandoned.

Recently it has been discovered that a fluidized bed of magnetizableparticulate solids can be stabilized when operated under the influenceof a magnetic field, and that such a bed is useful for conductingvarious fluid-solids contacting processes; inclusive particularly ofadsorption, absorption, particulate removal and catalytic processes.Notable among these are gas-solids contacting processes primarilydesigned for particulate capture but which may also feature a catalyticreaction, or reactions; or the process may be primarily designed forconducting a chemical reaction, or reactions, with or without thefeature of particulate capture. Processes of this type are conductedwith composites wherein a ferromagnetic component is incorporated withthe nonferromagnetic component, or components, to render the compositeferromagnetic.

Like conventional fluidized processes a fluid, notably a gas, isinjected upwardly at velocity sufficient to overcome the free fallvelocities of the individual particles (due to gravity) and cause bedexpansion and fluidization of the particles without sweeping significantamounts of the particles, catalytic or otherwise, from the bed. Inconventional fluidized processes, however, the injection of gas atvelocity sufficient to produce expansion of the bed (i.e., transform thefixed bed from a fixed packed bed to a fluidized bed) is accompanied bysignificant bubble formation whereas, in contrast, in a fluidized bedsubjected to the influence of a magnetic field at conditions which doesnot increase the weight of the bed there exists an interim, or quiescentzone wherein there is little, if any, motion exhibited by the particleswithin the fluidized bed. Thus, within this zone the formation ofbubbles and slugs are virtually eliminated due to the interactionbetween the fluidized ferromagnetic particles and the magnetic field;operation within such zone characterizing that of a magneticallystabilized bed.

Magnetically stabilized bed processes offer advantages over both fixedand fluidized bed operations. They provide superior operation overconventional fluidized bed operations in that they provide bettercounter-current contacting, low gas and solids back mixing, and lowerparticle attrition. They provide better operation as contrasted withfixed bed operations in that they provide lower pressure drop, betterability to transfer solids, and virtually eliminate bed pluggingproblems. A process disclosing a magnetically stabilized bed and itsmode of operation for conducting catalytic reactions, and the capture ofparticulates to provide a filtering action is disclosed in U.S. Pat. No.4,115,927 by Ronald E. Rosenweig.

Catalyst composites comprised of ferromagnetic inclusions dispersedwithin matrices constituted in part of nonferromagnetic materials andthe subjection of beds of such particles to the influence of a magneticfield are known; albeit much of the early work dating back over the lastdecade was done with particulate ferromagnetic materials which were notcatalytically active, or possessed of only limited catalytic activity.Thus, e.g., iron powder or steel balls, were of questionable merit ascatalysts; or if catalytic to a limited extent, then the ferromagneticcomponent constituted essentially the whole of the catalyst. In anyregard, a reference by Ivanov et al, Zhurnal Prikladoni Khimii, 43,2200-2204 (1970) describes catalytic particles characterized as Fe₂ O₃(88.16%), apparently the gamma phase of Fe₂ O₃ which is magnetic, whichwere collected together to form a bed and subjected to the influence ofa magnetic field. Ivanov et al, Comptes rendus de l'Academie bulgare desScience, Tome 23, No. 7, 787-790 (1970) discloses a fluidization processusing a ferrochrome catalyst for the conversion of carbon oxide withwater vapor in a magnetic field. U.S. Pat. No. 4,115,927, supra,discloses the use of a ferromagnetic nickel containing catalyst,supplied commercially by Chemetron Corporation known as Girdler G87RS ina magnetically stabilized fluidized bed. The catalyst is 40 wt. % nickelon an alumina support, prereduced and stabilized by the manufacturer.Known catalysts of magnetic character are thus characterized as systemswherein irregular shaped ferromagnetic particles, effectivelyapproximating spherical shape, are dispersed in admixture withnonferromagnetic particles, or catalyst composites comprised offerromagnetic particles effectively of approximately spherical shapeincorporated as inclusions within nonferromagnetic materials which actas matrices for the ferromagnetic inclusions.

Whereas magnetically stabilized bed processes which utilize catalystscontaining irregular shaped ferromagnetic inclusions, have proven usefulin conducting various chemical reactions, notably hydrocarbon conversionreactions, their performance nonetheless falls far short of providingpractical, economic commercial gas solid contacting processes. Simplystated, too much energy (and consequently too much cost) is required tomaintain an effective magnetic field. Even in the use of a catalystwhich contains a high concentration of particles, or inclusions of goodferromagnetic properties which ab initio may be sufficiently magnetic tomeet borderline economics, the magnetic properties of the catalystgenerally fade and grow poorer as the time of the operation is continuedand extended. The problem is intensified due to shock, thermalexcursions, or the like such that the bed of catalytic particles isgradually demagnetized as the time of operation of the process isextended.

The magnetization achieved when a ferromagnetic component is placed inan applied field depends on the nature of the ferromagnetic component,the effective field strength, and the magnetic history of the material.The principal variable available to control the extent of magnetizationof a specific ferromagnetic material is the effective field strength.The effective magnetic field strength, H_(e), applied across a bed isequal to the (empty vessel) applied magnetic field strength, H_(a),diminished by a factor dM, which can be mathematically stated, asfollows:

    H.sub.e =H.sub.a -dM                                       (1)

where d is taken as a demagnetization coefficient (0<d<1) related togeometry, and M is the magnetization of the bed. It is thus highlydesirable to achieve a high value of H_(e) and consequent high value ofM, while using as low of an applied field H_(a) and consequent energyexpenditure as possible. Thus, it is desirable to employ a bed geometrywith as low a value of d as possible.

In the light of the known art then a pertinent consideration for theefficient operation of a magnetically stabilized bed was the over-allbed, particularly the shape or geometry of the bed itself as opposed toa consideration of the particles themselves. Thus, the bed per seconstituted a macro-particle, and its shape was the pertinent factor forconsideration in the development of a more efficient process, not theshape or geometry of the particles per se which were mere constituentsof the macro-particle, or bed. In accordance with this concept thedemagnetization coefficient d was related to bed geometry, and themagnetization M was the volume average of magnetization of the bed. Thisthen led to the conclusion that bed geometries having long dimensions inthe direction of the field and short dimensions perpendicular to itwould have low values of d, which was desirable. Or, conversely stated,it was concluded that bed geometries having long dimensionsperpendicular to the field and short dimensions parallel to it wouldhave large values of d, which was undesirable. A consideration of thevalue of M also leads to the conclusion that the magnetically stabilizedfluidized bed, and associated magnetizing equipment, should have largedimensions in the direction of the field and small dimensionsperpendicular to the field.

Composite magnetic catalysts, however, have proven far more difficult tomagnetize than expected. Pure ferromagnetic components show roughly theexpected behavior, saturating at the proper value and, when correctedfor demagnetization, show high susceptibilities. Composites which arecomprised of admixtures of ferromagnetic and nonferromagneticcomponents, or composites which contain ferromagnetic inclusions, alsosaturate at the proper values, but show low susceptibilities, even whencorrected for demagnetization. Applied fields required to achieve agiven magnetization have proven to be of magnitude considerably higherthan predicted, and quite unfeasible for commercial operations.

The difficulty with the prior art theory therefore is that it failed toconsider, much less provide an understanding or appreciation of thesignificance of the geometry of the particle itself. Whereas prior arttheory would lead to a desire for a bed with a low value of d, itnevertheless failed to permit such an achievement. The sum-total of thevarious particles used in the formation of the magnetically stabilizedfludized beds of the prior art provided values for d_(f), ademagnetization coefficient based on inclusion shape, as hereinafterdiscussed, of about 1/3. Such values for d_(f), as suggested, however,do not permit commercially feasible operations in fluid-solidscontacting processes.

It is, nonetheless, the primary objective of the present invention toobviate the foregoing and other disadvantages of processes which utilizemagnetically stabilized fluidized beds for fluid-solids contacting,inclusive particularly of adsorption, absorption, particulate removaland catalytic processes.

A particular object is to provide a magnetically stabilized fluidizedbed process across which an external magnetic field can be moreeffectively applied, i.e., to achieve higher magnetization at a givenapplied field and ferromagnetic component; or the same applied fieldwith a component possessing less ferromagnetism or a less magneticallysusceptible component; or combination of such effects.

A further object is to provide a magnetically stabilized fluidized bedprocess which utilizes a bed of ferromagnetic solids particlesconstituted of one or more ferromagnetic inclusions dispersed within anonferromagnetic matrix material across which a field can be applied ina manner which provides lower demagnetization coefficients.

A more specific object is to provide composites of particulate materialwherein magnetically soft ferromagnetic inclusions are dispersed in amatrix of nonferromagnetic material, inclusive particularly ofcomposites of such character which also contain a catalytically activecomponent, or components, these composites being particularly useful inmagnetically stabilized fluidized beds for conducting gas-solidscontacting, or for conducting catalytic reactions, or both.

These and other objects are achieved in accordance with the presentinvention which, in general, embodies:

(A) a composition, or article of manufacture, characterized as aparticulate material which can be oriented within, and formed into amagnetically stabilized fluidized bed to provide an effectivedemagnetization coefficient significantly less than 1/3, suitably ademagnetization coefficient, d_(f), ranging from about 0.0027 to about0.174, preferably from about 0.022 to about 0.108, which comprises:

(i) particles of average size ranging from about 10 micrometers (μm) toabout 4000 μm, preferably from about 50 μm to about 500 μm, eachcontaining a nonferromagnetic component, or components, and preferably acatalytically active component, or components, composited with a singleelongated ferromagnetic component, the ferromagnetic component beingmultidomain, having dimensions of at least 1 μm in all directions and alength:diameter (L/D) ratio of at least 2 but not more than 17.3, saidferromagnetic component being present in the composite particles as aninclusion within a nonferromagnetic matrix, a ferromagnetic inclusionbeing sufficiently spaced apart in the particulate composite thatessentially any ferromagnetic inclusion can be circumscribed in animaginary sphere which does not include or intersect any otherferromagnetic inclusion of said particulate composite, saidferromagnetic inclusion constituting at least 0.5%, preferably at least5%, but not more than 3/2(L/D)² of the total volume of each particle,where the L/D ratio is the ratio of the longest dimension of theferromagnetic inclusion relative to the shortest dimension, and theparticles can, in said magnetically stabilized fluidized bed rotate, orturn to line up the long dimensions of the ferromagnetic componentsparallel to the direction of the field and a short dimensionperpendicular to the direction of the field; or

(ii) particles of average size ranging from about 10 micrometers (μm) toabout 4000 μm, preferably from about 50 μm to about 500 μm, eachcontaining a nonferromagnetic component, or components, and preferably acatalytically active component, or components, and within each of whichis composited a plurality of elongated ferromagnetic components, aferromagnetic component being multidomain, having dimensions of at least1 μm in all directions, elongated in one or two dimensions, and having alength:diameter (L/D) ratio of at least 2 but not more than 313,preferably not more than 30, said ferromagnetic components being presentin the composite particles as inclusions within a nonferromagneticmatrix, arranged in such a way that essentially any ferromagneticinclusion can be circumscribed in an imaginary sphere which does notinclude or intersect any other ferromagnetic inclusion, and oriented insuch a way that there is a preferred direction in each particle suchthat all the ferromagnetic inclusions in that particle have a longdimension essentially parallel with said preferred direction andconstituting at least 0.5%, preferably at least 5%, but for particleselongated in one dimension not more than 2π/3(L/D+1)², and for particleselongated in two dimensions not more than π/2(L/D+1), of the totalvolume of each particle, where L/D is the average ratio of the longestdimension of a ferromagnetic inclusion relative to its shortestdimension, and, in said magnetically stabilized fluidized bed, theparticles can rotate, or turn to line up said preferred directionparallel to the direction of the field such that essentially all of theferromagnetic inclusions have a long dimension essentially parallel tothe direction of the field; and

(B) A process wherein the plurality of composite particles ascharacterized in (A)(i) and (A)(ii), supra, is formed into amagnetically stabilized fluidized bed, and oriented in said magneticfield to provide a demagnetization coefficient, d_(f), significantlyless than 1/3, suitably a demagnetization coefficient ranging from about0.0027 to about 0.174, preferably from about 0.022 to about 0.108.

It has been found that the shape of the individual ferromagneticinclusions of a composite structure is far more important than the shapeof the bed in the operation of magnetically stabilized fluidized bedprocesses. The ferromagnetic inclusions of a composite particle aresufficiently spaced apart from other ferromagnetic inclusions that they,when formed into a bed and subjected to a magnetic field with the axesof the ferromagnetic inclusions aligned parallel to the field, willprovide far higher magnetization in a given applied field than particlesotherwise identical and similarly dispersed except that the elongateferromagnetic inclusions are spherical or of irregular shape asdisclosed in prior art processes.

The ferromagnetic inclusions, as practiced in accordance with thisinvention are of essentially any shape, regular or irregular wherein atleast one dimension is considerably longer than another. Particlescontaining such inclusions can be oriented within the field to provide ademagnetization coefficient d_(f), considerably less than 1/3. Shapeswherein the ferromagnetic inclusions are spherical, or such shapes whichare effectively spheroid cannot be used. Nonoriented ferromagneticinclusions, not truly spherical in the geometrical sense, may yetcontain deviations from sphericity which are randomly directed andcancel each other so that they are, in effect spherical; and the sphere,with equal dimensions in all directions, has a demagnetizationcoefficient d_(f) equal to one-third which is unusable. Theferromagnetic inclusions are preferably of cylindrical shape, oblatespheroids, or extremely prolate spheroids. The ferromagnetic inclusions,used in the magnetically stable fluidized beds, thus necessarily haveeffective L/D ratios considerably greater than unity, and providedemagnetization coefficients d_(f) significantly less than 1/3. Thepreferred shapes are thus those having considerably high L/D ratios,suitably L/D ratios ranging at least 2:1, preferably L/D ratios rangingfrom about 3:1 to about 313:1. Specifically, (1) for a plurality ofparticles, each containing a single elongated ferromagnetic inclusionthe L/D ratio ranges to about 17.3:1, preferably 5.5:1; (2) for aplurality of particles, each containing a plurality of ferromagneticinclusions elongated in one dimension the L/D ratio ranges to about19.5:1, preferably 5.5:1; and (3) for a plurality of particles, eachcontaining a plurality of ferromagnetic inclusions elongated in twodimensions the L/D ratio ranges to about 313:1, preferably 30:1.Particles having an L/D ratio of at least 2:1 provide a demagnetizationcoefficient, d_(f), of about 0.174, or less; particles having L/D ratioswithin the ranges 3:1 to 100:1 provide demagnetization constants rangingabout 0.108, or less; and those having L/D ratios within the ranges 4:1to 20:1 provide demagnetization constants ranging 0.075, or less. Thepreferred composite particle is of roughly spherical shape and has anaverage diameter ranging from about 10 μm to about 4000 μm, preferablyfrom about 40 μm to about 500 μm.

It is essential to use the externally applied field effectively toachieve high effective magnetization with any given ferromagneticcomponent. Or, stated alternatively, it is necessary in terms ofcommercial reality that a ferromagnetic component exhibit high inducedmagnetism in a small applied field. Conventional wisdom, however, wouldlead to the belief that the individual ferromagnetic inclusions wouldinteract so much with each other that, in a magnetically stabilizedfluidized bed, the over-all effect would be that of a large bar magnet.For example, in considering the action of a magnetic field on a barmagnet it is found that a soft ferromagnetic material can be magnetizedwhen a magnetic field H is applied, and that a magnetic moment m isinduced in the sample, which is related to the magnetization M byM=4π(m/V). This moment is due to current loops from unpaired electrons,but an equivalent and often useful viewpoint is that it is due to theseparation of pairs of magnetic poles. The usefulness of this viewpointlies in the fact that 4π lines of the H field terminate on each magneticpole. However, it is the strength of H inside the ferromagnet whichdetermine the magnetic moment, and all ferromagnets of similar material,which have the same magnetic moment [(number of poles)X(separation)],must have the same field strength H inside. For example, a bar magnetfour units in length and one unit in width may contain two north polesand two south poles four units in length apart, and another of similarsize may contain eight north poles and eight south poles one unit apart.Thus, although both have the same moment, the latter would be capable ofcancelling 32π lines of H with its poles, and hence far more appliedfield is required to magnetize it than the other, which can cancel only8π lines. One would thus expect a bed with the long dimension alignedwith a field, or horizontally aligned bed to be superior to a bed havingits long side vertically aligned with the field.

The amount of field lost, it would also be expected, would depend on thegeometry of the bed through the demagnetization coefficient d, inaccordance with model H_(e) =H_(a) -dM, supra. It has been found,however, that this model approximates objective reality for particlecompositions which contain ferromagnetic inclusions withnonferromagnetic components, only when the ferromagnetic inclusions arepresent in high concentrations. The model is not valid for beds whichcontain the ferromagnetic inclusions in dilute concentration as requiredfor catalysts for use in magnetically stabilized fluidized bedoperations. Applicant, however, after considerable experimentation,study and rejection of this and various other models has discovered thatthe geometry for mathematical equation (1), supra, is that of theindividual ferromagnetic inclusion, and its magnetization, not themagnetization of the entire bed.

Applicant feels no necessity, and therefore no desire of being bound byany specific theory of mechanism, but is nonetheless quite confidentthat he has formulated a model which adequately explains the truephenomena which are occurring in a fluidized bed of ferromagnetic solidsoperated under the influence of a magnetic field. In accordance withthis model every individual ferromagnetic inclusion actually "sees," orexperiences, the same external field, as opposed to the gross bedconcept. Accordingly, a model which conforms to objective reality mustinclude a term d_(f) M_(f), wherein the terms d and M are as previouslyidentified, and the subscript f is an average value of a ferromagneticinclusion, rather than an average value taken over the entire bed. Themagnetic field experienced by an inclusion has been found to conformsubstantially to that within a Lorentz polarization sphere.

Dielectric materials placed in an electric field, in accordance with thenew model developed by Lorenz formulation, form induced electric poles,which cancel part of the applied electric field, exactly as magneticpoles cancel applied magnetic field. The amount of field cancelled isrelated to sample geometry and polarization, P, by exactly the samedemagnetization (depolarization) coefficient,

    E.sub.internal =E.sub.external -d(4πP)                  (2)

except that the 4π factor is included in the definition of M and not ofP.

The Lorentz polarization sphere, which relates to a consideration of thedielectric properties of a substance, formulates quite imaginatively thelocal field applied to a small spherical cavity cut out of a specimenaround a reference point. It constitutes a measurement of the totalelectric field applied at the reference point and takes into account thefield applied from external sources, the field of the polarizationcharges on the surface of the specimen, the depolarization field whichresults from polarization charges on the outer surface of the sphericalcavity, and the field of the atoms within the cavity which constitutesthe total effect at one molecule of the dipole moments of all of theother molecules in the specimen.

A well-known problem in classical electricity relates the polarizationof a dielectric to the polarizability of an individual molecule and thelocal electric field at that molecule. An imaginary spherical cavity isdescribed, centered on the molecule of interest. Other molecule dipolesoutside the cavity are treated on an average basis, according to theircontribution to the surface charges on the imaginary cavity. Thedepolarization field due to these charges was first calculated byLorentz and equals -1/3(4πP). Contributions to the electric field at themolecule by dipoles inside the cavity are summed on an individual basis.This leads to a depolarization effect d(4πP) by the surface of thespecimen, -1/3 (4πP) by the surface of the cavity, and the electricfield E₃ by all the dipoles inside the cavity,

    E.sub.local =E.sub.external -d(4πP)+1/3(4πP)-E.sub.3 ( 3)

An exactly analogous treatment can be used for demagnetization in anmagnetic stabilized fluidized bed wherein all of the ferromagneticinclusions in a magnetic stabilized fluidized bed are considered as aLorentz sphere which encloses exactly one inclusion. The magnetic fieldinside the particle is calculated in a manner analogous to that employedin calculating a local electric field. Outside the sphere, far enoughfrom the particle to be averaged, the average magnetization of the bedis M_(b). Inside the sphere, on a microscopic basis, the magnetizationis zero everywhere except inside the inclusion, where it is M_(f). Theonly difference from the electrostatic case is that the particles arefar enough apart that inside the cavity the only demagnetization effectis that due to the particle of interest, d_(f) M_(f). So the magneticanalogy to equation (3) is

    H.sub.e =H.sub.1 -d.sub.b M.sub.b +1/3M.sub.b -d.sub.f M.sub.f ( 4)

This procedure provides a correct value of H_(e) which is related toM_(f) only by the intrinsic magnetic properties of the ferromagneticcomponent. In previously known magnetically stabilized beds the termd_(f) M_(f) has been much larger and more significant than d_(b) M_(b)or 1/3 M_(b).

The applied field H_(a) and magnetic moment m can be directly,experimentally determined, so that d_(b) and M_(b) can be calculated byfurther determination of sample volume and shape. Thus, the first threeterms on the right side of equation (4) can be readily experimentallyevaluated. The term M_(f) is found to depend on the volume percent ofthe ferromagnetic component, and d_(f) on inclusion shape and degree oforientation. The relationship between H_(e) and M_(f) is found to dependcritically on inclusion purity and heat treatment. Rearranging equation(4) to put all unknown quantities on the left,

    H.sub.e +d.sub.f M.sub.f =H.sub.s =H.sub.a -(d.sub.b -1/3)M.sub.b ( 5)

where it can be explicitly recognized that each side of the equation isa measure of H_(s), the cavity magnetic field which, though it producesa magnetic field strength inside the Lorentz sphere, it is nonethelessoutside the particle of interest.

The usefulness of equation (5) in the new model is in relating M_(p),the magnetization of a particle, averaged over the particle, includingthe ferromagnetic component, support, active catalytic component, orcomponents, and pore volume but not the interstitial void volume of thebed. Calculating M_(p) from m and H_(a) involves corrections for voidageand sample geometry, which can be measured. M_(p) is related to M_(f)and H_(e) through volume percent, inclusion shape and orientation, andinclusion intrinsic magnetization parameters. Therefore, just as therelationship between H_(e) and M_(f) for a given sample is invariant, sothe relationship between H_(s) and M_(p) for a given sample isinvariant. It is the right equality in equation (5), not equation (1),that predicts how M_(p) responds to changes in sample shape and voidage.

To summarize, H_(a) and m can be measured, and using known auxiliaryconstants, H_(s) and M_(p) can be calculated, to wit:

    M.sub.p =4πρ.sub.p m/W,                             (6)

    H.sub.s =H.sub.a -(d.sub.b -1/3)(1-ε.sub.o)M.sub.p ( 7)

where ρ is the density, m is the magnetic moment, W is the mass andε_(o) is the void fraction. Enough pairs (H_(s), M_(p)) can be measuredto determine the functional relationship between H_(s) and M withacceptable accuracy. Then in the magnetic stabilized bed, with new,known values of H_(s), d_(b), and ε_(o), that relationship can be solvedsimultaneously with equation (7) to give the unknown values, H_(s) andM_(p).

Every inclusion thus "sees" the same external field H_(s), as given inequation (7), and each of the terms H_(e) and M_(f) is a function of thed_(f) of the inclusion. Every inclusion has a different d_(f), and H_(e)and M_(f) can be increased within an applied field of given fieldstrength by the production of particles having a low d_(f). Suchparticles have a long dimension parallel to the field.

The present process, and compositions, are useful in various processesinclusive particularly of adsorption, absorption, particulate removaland catalytic processes. The compositions are particularly useful asfilters for the removal of contaminant particles from a gas stream,whether or not the particles additionally function as catalysts. Theprocess, and compositions, are also particularly useful in conductinghydrocarbon conversion reactions illustrative of which are fluidhydroforming (reforming), catalytic cracking, isomerization, coking,polymerization, hydrofining, alkylation, partial oxidation,halogenation, dehydrogenation, desulfurization, reductions, gasificationof coal, fluid bed combustion of coal, coal liquefaction, retorting ofoil shale and the like.

In the preparation of particulate solids, or catalysts for use in thepractice of this invention it is essential that the elongateferromagnetic particles present in an aggregate of the particles, or asinclusions within a composite, be spaced apart one from another,separated, or present in dilute concentration so that each experiencesthe applied field.

Specifically, essentially each ferromagnetic inclusion should besufficiently separated from all others that an imaginary sphere, theLorentz sphere, can be circumscribed around it, which neither includesnor intersects any other ferromagnetic inclusion, around saidferromagnetic inclusion. Simple geometrical considerations show thatthis condition imposes an upper limit to the volume fraction of theferromagnetic inclusions in each composite particle, depending on thespecific embodiment of the invention, as follows: (1) for a plurality ofparticles, each containing a single elongated ferromagnetic inclusion,approximating the shape of the inclusion as a cylindrical needle oflength L and diameter D, the upper limit is 3/2(L/D)² ; (2) for aplurality of particles, each containing a plurality of ferromagneticinclusions elongated in one dimension, approximating the shape of theinclusions as cylindrical needles of average length L and diameter D,the upper limit is 2π/3(L/D+1)² ; and (3) for a plurality of particles,each containing a plurality of ferromagnetic inclusions elongated in twodimensions, approximating the shape of the inclusions as cylindricaldiscs of diameter L and thickness D, the upper limit is π/2(L/D+1). Thefurther requirement that the elongation L/D shall be at least 2necessarily sets absolute upper limits on the volume fraction of theferromagnetic inclusions as follows: (1) 37.5%; (2) 23.3%; and (3)52.4%, respectively, supra. Likewise, the requirement that theferromagnetic inclusions constitute at least 0.5%, and preferably 5%, ofthe volume of the particles sets upper limits on the elongation of theferromagnetic inclusions as follows: for ( 1), supra, L/D cannot exceed17.3, preferably 5.5; for (2), supra, L/D cannot exceed 19.5, preferably5.5; and for (3), supra, L/D cannot exceed 313, preferably 30,respectively.

It is essential in the formation of particulate solids, or catalysts,that the elongate ferromagnetic inclusion, or inclusions be dispersedwithin the nonferromagnetic material such that it serves as a matrix, orcontinuous phase surrounding said inclusion, or inclusions. In theformation of catalysts, it is also essential that the catalyticcomponent, or components, be well dispersed upon the surface of theparticles in catalytic amounts. The catalytic component, or components,is dispersed to a high surface area state upon the surface of theparticles; the particles serving the same function as conventionalcatalyst supports. In a catalytically effective state of dispersion, acatalytically active concentration of the catalytic component, orcomponents, is present on the surface of the particles in essentiallyatomically dispersed form, as defined by the size of the crystals of thedispersed catalytic component, or components (length of a side of anassumed cubic crystallite).

The matrix portion of particles is preferably constituted of arefractory porous inorganic oxide. The matrix material constitutes asupport with which the catalytic component, or components, iscomposited, in catalytically effective amount, suitably formed bycogellation with a catalytic metal component, or components, or byimpregnation of the particles with a solution which contains a solublecompound, or compounds, of the metal, or metals. The matrix material canbe constituted of, or contain, for example, one or more of alumina,bentonite, clay, diatomaceous earth, zeolite, silica, magnesia,zirconia, thoria, and the like. The most preferred matrix material isalumina to which, if desired, can be added a suitable amount of otherrefractory carrier materials such as silica, zirconia, magnesia,titania, etc., usually in a range of about 1 to 20 percent, based on theweight of the support. Exemplary of a matrix material for the practiceof the present invention is one having a surface area of more than 50 m²/g, preferably from about 100 to about 300 m² /g, and higher, a bulkdensity of about 0.3 to 1.0 g/ml, and higher, an average pore volume ofabout 0.2 to 1.1 ml/g, and an average pore diameter ranging about 30 Ato about 300 A, and higher.

Essentially any catalyst component, or components, can be compositedwith the particles dependent upon the type of reaction which is to becarried out. For example, in conducting hydrocarbon conversionreactions, e.g., a hydroforming (reforming, with hydrogen) reaction, acatalyst can be formed which comprises a composite of a refractory orinorganic oxide support material, particularly alumina, and a Group VIIInoble metal hydrogenation-dehydrogenation component (Periodic Table ofthe Elements, Sargent-Welch Scientific Company, Copyritht 1968), e.g.,ruthenium, rhodium, palladium, osmium, iridium or platinum, notablyplatinum, to which a promoter metal, e.g., rhenium, iridium or the likemay be added to promote the activity and selectivity of the catalysts.Suitably, the reforming catalyst, or composite also contains an addedhalogen component to provide acidity, particularly fluorine or chlorine,and preferably the promoter component is introduced into the support, orcatalyst, by impregnating same with a solution comprising a soluble saltor compound thereof.

In reforming operations, it is desirable that the sulfur concentrationin the naphtha feed not exceed about 10 parts, and preferably should notexceed about 5 parts, per million parts of feed. At theseconcentrations, poisoning of the catalyst can usually be avoidedprovided that sufficient hydrogen is added or recycled to strip out thesulfur, as hydrogen sulfide, from the reaction mixture. By maintaininglow sulfur in the feed and a sufficiently high recycle gas ratetherefore, sulfur accumulation and consequent catalyst poisoning can beavoided.

The present compositions are also particularly suitable for conductinghydrofining reactions, which refers to the catalytic hydrogenation ofsolvents and distillate fuels. Hydrofining is employed to remove sulfur,nitrogen and other nonhydrocarbon components, as well as to improve theodor, color, stability, engine cleaniness and combustioncharacteristics, and other important quality characteristics.Sulfur-containing naphtha feedstocks as used in reforming are generallyhydrofined without substantial hydrocarbon conversion in the presence ofsulfur (and nitrogen) tolerant catalysts, e.g., a Group VI-B or VIIImetal catalyst such as cobalt molybdenum on an alumina-silica base tosubstantially eliminate the sulfur. When applied for processingcatalytic cracking feedstocks, hydrofining significantly reduces carbonyield, increases gasoline yield, and improves the quality of thecatalytic cracking stocks.

The catalysts employed in hydrofining are comprised of composites ofgroup VI-B or Group VIII metal hydrogenation (hydrogen transfer)components, or both, with an inorganic oxide base, or support, typicallyalumina. Typical catalysts are molybdena on alumina, cobalt molybdate onalumina, nickel molybdate or nickel tungstate on alumina. The specificcatalyst used depends on the particular application. Cobalt molybdatecatalysts, are often used when sulfur removal is the primary interest.The nickel catalysts find application in the treating of cracked stocksfor olefin or aromatic saturation. Sweetening (removal of mercaptans) isa preferred application for molybdena catalysts.

The typical catalytic cracking process unit is one wherein a gas oilfeed is cracked in a cracking zone at elevated temperature in thepresence of a cracking catalyst, the catalyst is regenerated in aregeneration zone by burning coke off the catalyst, and the catalyst iscirculated between the cracking zone and the regeneration zone. Suitablecracking catalysts for the practice of the present invention compriseoriented elongate ferromagnetic inclusions incorporated within suchcatalysts. Suitable cracking catalysts include conventional silica-basematerials which, preferably, contain bulk porous alumina dispersedtherein. Illustrative of such catalyst are, e.g., amorphoussilica-alumina; silica-magnesia; silica-zirconia; conventional claycracking catalyst, etc. The amorphous gel silica-metal oxide crackingcatalyst may further be composited with kaolin in amounts of about 10 to40 wt. % (based on total weight of the composited catalyst) and up to 20wt. % or more crystalline alumino-silicate zeolite, such as faujasite.

Silica and alumina base catalysts, especially the latter, areparticularly suitable for conducting a wide range of reactions. Silicabased cracking catalyst including naturally occurring activated claysand synthetic prepared composites have long been recognized as pathsuseful in promoting catalytic hydrocarbon reactions. Siliceous catalystscontain silica and frequently one or more promoting metal compounds suchas one or more oxides or sulfides of a Group VI-B metal (e.g.,molybdenum or tungsten) either alone or in admixture with a Group VIIImetal compound, specifically an oxide or sulfide of nickel or cobalt.Active catalysts are also obtained by depositing such Group VI-B and/ora Group VIII metal compound on an inorganic oxide, preferably an aluminasupport or a support comprising a combination of silica and alumina.Likewise other promoting oxides such as zirconia and magnesia may beemployed in conjunction with a support containing silica and/or alumina.

The catalysts of this invention may be in the form of powder, beads,tablets, pills, or pellets or extrudates depending upon the type ofprocess. Composites with highly elongated ferromagnetic inclusions,permit the use of low practical fields for commercial magneticallystabilized fluidized bed reactions. The use of ferromagnetic inclusions,elongated along one axis to provide needle-like shapes, or along twoaxes to provide flat plate-like shapes provide the desired improvements.Various ferromagnetic substances, including but not limited to magnetiteFe₃ O₄, γ-iron oxide (Fe₂ O₃), ferrites of the form XO.Fe₂ O₃, wherein Xis a metal or mixture of metals such as Zn, Mn, Cu, etc.; ferromagneticelements including iron, nickel, cobalt and gadolinium, alloys offerromagnetic elements, etc. if of elongate shape may be used asferromagnetic inclusions. Nonmagnetic materials can be coated with ordispersed within solids having the quality of ferromagnetism to providethe ferromagnetic inclusions. Generally, a ferromagnetic composite isincorporated with a nonmagnetic catalytic material, and the fluidizedbed containing such composites can also include particulate solids whichare nonmagnetizable. The longest side of the ferromagnetic particles orinclusions can range to 4000 micrometers (μm), and higher, but generallyrange from about 2 to about 1000 μm, preferably from about 50 μm toabout 500 μm. The smaller diameter of the particles generally rangesfrom about 0.5 to about 500 μm, preferably from about 1 to about 100 μm.In order for each ferromagnetic inclusion to behave as a typicalferromagnet, independently experiencing the magnetic field, it isnecessary that each inclusion contain multiple magnetic domains. Thisrequirement is generally met if all dimensions of the inclusion exceed 1μm. Smaller ferromagnetic particles, containing only one magneticdomain, behave as permanent, hard, magnets even if they are composed ofmagnetically soft material, and do not respond smoothly or reproduciblyto the applied field. A preferred technique for providing the elongatedor oriented ferromagnetic particles for use as inclusions is by physicalshaping methods, e.g., by the ball milling of a ferromagnetic metallicpowder, e.g., iron, iron alloys such as steel, cobalt, alloys of cobalt,nickel, alloys of nickel and the like.

Particles, each of which contains a single elongated ferromagneticinclusion, can be prepared by fluidizing a suitable elongatedferromagnetic powder in a conventional fluidized bed, using anysufficiently nonreactive gas, such as air, nitrogen, carbon dioxide,etc., for fluidization. The upper portion of the bed can be heated tomaintain the top bed temperature in the range of about 140° F. to about390° F., while a nozzle, or nozzles, near the bottom of the bed spray afine mist of alumina sol into the fluidized mass of particles along withthe fluidizing gas. The mist deposits on the individual ferromagneticparticles, and as they move to the top of the bed the sol is dried toform an alumina precursor, such as boehmite, AlO(OH). The particles moveback to the bottom of the bed where they are coated with more aluminasol, and this process is continued until the desired amount of aluminaprecursor has been deposited; the surface tension in the alumina solcausing the finished particles to have a substantially spherical shape.The normal turbulence on a conventional fluidized bed is maintainedsufficient to transport the particles back and forth between the top andbottom of the bed, and the sol addition rate is maintained low enough,and sufficient to keep particles from agglomerating. Radio frequencyinduction heating can provide a convenient way to heat the top of thebed while eliminating any tendency of the particles to stick toheat-transfer surfaces. When the desired amount of alumina precursor hasbeen deposited, the particles are finished by calcining to convert theprecursor to alumina, either in a separate vessel, or simply byincreasing the power to the radio frequency in the induction coils.

Alternatively, a suitable ferromagnetic material can be mixed with anaqueous solution of aluminium hydroxychloride and hexamethylenetetramine, in concentrations such that the finished alumina particleswill contain on the one hand, an average substantially less than oneferromagnetic inclusion per particle. Droplets of the mixture are addedto the top of a hot oil column kept at about 190° F., surface tensioncausing the droplets to take a spherical form, but particle elongationcan be produced by increasing the applied field. The heat causes thealumina solution to gel before the elongated droplets reach the bottomof the column. Magnetic separation is used to separate those particleswhich do contain one ferromagnetic inclusion from those which do not.The selected, desired particles are further cured and calcined, whilethose which are not are repeptized with dilute hydrochloric acid andrecycled as starting material. This second preparation method is moresuitable for particles containing a relatively low volume fraction offerromagnetic inclusion, while the first preparation is more suitablefor preparing particles which contain a relatively high volume fractionof ferromagnetic inclusion. On the other hand, of course, particles canbe made which contain a plurality of ferromagnetic inclusions byincreasing the concentration of ferromagnetic inclusions in the dropletsadded to the top of the hot oil column. A magnetic field can be appliedacross the column to cause parallel orientation of the ferromagneticparticles which, as the particles congeal, become parallelly orientedinclusions within an aluminum matrix.

The invention will be more fully understood by reference to thefollowing selected nonlimiting examples and comparative data whichillustrate its more salient features. All parts are given in terms ofweight units except as otherwise specified.

The following Examples 1 and 2 are reference demonstrations based on theprior art. Example 1 shows that for randomly oriented materials theparticle magnetization is a function of the concentration of themagnetic component as long as the concentration is not too high. Themaximum concentration examined was 78 wt. %. Example 2 shows that at92.3 wt. % concentration of stainless steel on alumina, particle toparticle interactions start to occur that lower the magnetic moment ofthe particles.

EXAMPLE 1

Magnetic composite materials were prepared from atomized 410 stainlesssteel powder in a range of concentrations, matrices, and particle sizes.Preparative techniques included: (1) mixing the 410 stainless steelpowder with a silica-alumina gel or an alumina gel and spray-drying themixture to form a composite powder, (2) spray-drying as in (1) and thencalcining the resulting powder; (3) mixing the 410 stainless steelpowder with alumina powder or polypropylene powder and pressing a pelletof the mixture in a hydraulic press; and (4) mixing the stainless steelpowder with silica-alumina gel and allowing the entire mixture to hardenin a tray, then crushing the resulting block to form a composite powder.Concentration of stainless steel in the finished composites varied from0.4 wt. % to 78 wt. %, and from 0.09 Vol. % to 39 Vol. %. In all cases,the volume percent stainless steel in the composite was substantiallyless than the volume percent stainless steel in the pure stainless steelpowder (47%), so that there was substantially no direct contact ofstainless steel particles within any of these composites. A very finemesh cut of the atomized stainless steel, with particle sizes from 0 to30 μm, was used in some preparations. A coarser cut, with particle sizesfrom 20 to 44 μm, was used in the other preparations. A total of 20different composites were prepared.

The magnetic properties of all these samples were measured using aPrinceton Applied Research Model 155 Vibrating Sample Magnetometer and aconventional laboratory electromagnet. Sample shape was varied as muchas the magnetometer sample holder would permit; all samples wereapproximately cylindrical, with their cylinder axis perpendicular to theapplied field in the magnetometer. Sample diameters could only be variedfrom 0.32 to 0.38 cm, but sample lengths were varied from 0.25 to 0.97cm.

It was found that stainless steel content was the only one of thesevariables that had a major influence on the magnetic properties of thecomposite. Magnetic moment at saturation was directly proportional tostainless steel content, with a proportionality constant of 171.5 emu/gstainless steel. In addition, the magnetic moment resulting when a givenfield was applied to an initially demagnetized sample was found to beprincipally determined by the stainless steel content. In particular,when an applied field of 200 oersteds was applied to each of the twentyinitially demagnetized samples, the induced magnetic moment averaged12.4 emu per gram of stainless steel in the sample, with a standarddeviation of only ±1.5 emu/g.

EXAMPLE 2

A composite sample was prepared by mixing 410 stainless steel powderwith alumina and pressing a pellet in a hydraulic press, just as inExample 1, except that the sample contained 92.3 weight percentstainless steel. Under the pressure of the hydraulic press, the samplewas compressed to the extent that it contained 56.6 volume percentstainless steel, somewhat greater than the original loose stainlesssteel powder. There was, therefore, extensive particle to particlecontact between the stainless steel particles in this composite. The0-30 μm mesh cut of 410 stainless steel powder was used in thiscomposite, the sample diameter was 0.322 cm, and the sample length was0.374 cm.

When this sample was demagnetized and a field of 200 oersteds wasapplied, the induced magnetic moment was only 8.9 emu per gram ofstainless steel, significantly lower than the value of 12.4 emu/g fromExample 1. This demonstrates that the magnetic interactions and magneticbehavior of magnetically dilute composites, where the magnetic particlesare substantially separated from one another, are qualitativelydifferent from the magnetic interactions and magnetic behavior ofmagnetically concentrated composites. Much, if not all, of the prior artteaching the advantages of orienting magnetic particles refers to highlyconcentrated magnetic materials. This invention, however, isspecifically directed to magnetically dilute particulate composites,containing (1) for a plurality of particles, each containing a singleelongated ferromagnetic inclusion less than 37.5 volume percent of theferromagnetic component; (2) for a plurality of particles eachcontaining a plurality of ferromagnetic inclusions elongated in onedimension less than 23.3 volume percent of the ferromagnetic components;and (3) for a plurality of particles, each containing a plurality offerromagnetic inclusions elongated in two dimensions less than 52.4volume percent of the ferromagnetic components.

The following Example 3 depicts the preparation and magnetic propertiesof nonoriented stainless steel ferromagnetic inclusions in an aluminabead.

EXAMPLE 3

A composite magnetic material in the form of beads was formed by mixing0-30 μm 410 stainless steel powder with an aqueous solution of aluminumhydroxychloride and hexamethylenetetramine, and then adding droplets ofthe mixture to the top of a hot oil column kept at about 190° F. Surfacetension caused the droplets to take a spherical form, and the heatcaused the alumina solution to gel before the droplets reached thebottom of the oil column. The product, after further curing, was a 410stainless steel/alumina composite in the form of spherical beads. Themagnetic behavior of one of these beads was determined. It contained39.4 wt. % (10.2 Vol. %) 410 stainless steel and had a diameter of 0.21cm. Its magnetic properties were found to be isotropic and substantiallythe same as the magnetic properties of the composites mentioned inExample 1. In particular, after being demagnetized, its magnetic momentat 200 Oe applied field was 10.6 emu per gram stainless steel.

The following Example 4 contrasts a bead with oriented ferromagneticinclusions with the bead of Example 3 containing random ferromagneticinclusions.

EXAMPLE 4

A composite magnetic material in the form of beads was prepared, insubstantially the same manner as described in Example 3, except that apermanent ring magnet was placed around the hot oil column near the topof the column. The presence of this magnet served to maintain an axialmagnetic field through about the top 50 cm of the column, with a maximumfield strength of about 300 oersteds. The magnetic field was intended toturn the 410 stainless steel particles and to orient them substantiallyparallel to the field, within their respective droplets, before thealumina in the droplets gelled. Once the alumina did gel, it wasexpected that the 410 stainless steel particles would be kept in thissubstantially parallel arrangement even after they were removed from themagnetic field.

Three beads which has been prepared in this manner were examinedindividually in a magnetometer. These beads were found to have highlyanistropic magnetic properties, with one direction of easy magnetizationand two mutually perpendicular directions of approximately equal hardmagnetization. Their properties are summarized in the following table.

                  TABLE                                                           ______________________________________                                                        First  Second   Third                                                         Oriented                                                                             Oriented Oriented                                                      Bead   Bead     Bead                                          ______________________________________                                        Wt. % 410 Stainless Steel                                                                       26.9     24.5     14.5                                      Vol. % 410 Stainless Steel                                                                      9.4      7.5      3.8                                       Diameter, cm      0.14     0.14     0.16                                      Magnetic Moment at 200 Oe                                                     emu/g SS                                                                      Easy Direction    26.2     26.0     30.7                                      Hard Direction    9.2      8.9      8.9                                       Improvements over Example 1,                                                  Ratio             2.1      2.1      2.5                                       ______________________________________                                    

It was also found that if these beads were placed in a magnetic fieldand were not restrained, they would spontaneously rotate until theirdirection of easy magnetization was substantially parallel to thedirection of said applied field. In a magnetically stabilized fluidizedbed, these beads would be free to turn in this manner. Therefore, in amagnetically stabilized fluidized bed at a given moderate applied field,beads prepared in this manner would have a magnetization 2 to 2.5 timesas great as similar beads prepared according to Example 3 due to thealignment of the stainless steel particles.

The following Example 5 depicts the further improved magnetic propertiesof beads made with oriented elongated steel particles.

EXAMPLE 5

A portion of the elongated 410 stainless steel powder from ballmillingwas incorporated into oriented composite beads according to the methoddescribed in Example 4, in which the bead formation is carried out inthe presence of a substantial magnetic field. The same permanent magnetwas employed to generate the magnetic field, and again it generated amaximum field strength of about 300 oersteds.

Two of the beads prepared in this manner were characterized in themagnetometer. As in Example 4, these beads were found to be highlyanistropic. Their properties are summarized in the table below.

    ______________________________________                                                         First    Second                                                               Oriented Oriented                                                             Bead with                                                                              Bead with                                                            Ballmilled SS                                                                          Ballmilled SS                                       ______________________________________                                        Wt. % 410 Stainless Steel                                                                        3.5        4.3                                             Vol. % 410 Stainless Steel                                                                       0.5        0.9                                             Diameter, cm       0.20       0.18                                            Magnetic Moment at 200 Oe                                                     emu/g SS                                                                      Easy Direction     51.0       41.2                                            Hard Direction     12.1       13.4                                            Improvements over Example 1,                                                  Ratio              4.1        3.3                                             ______________________________________                                    

This example demonstrates that magnetization in a magneticallystabilized fluidized bed can readily be increased by as much as a factorof at least three or four, by utilizing this invention.

It is apparent that various modifications and changes can be made in theconditions of operation, the identity of the ferromagnetic particle orinclusion used in forming the composite, the nature of the catalyticcomponent, or components, and manner of incorporation; and the likewithout departing the spirit and scope of the invention.

Having described the invention, what is claimed is:
 1. As a compositionof matter, particulate material which can be oriented within, and formedinto a magnetically stabilized fluidized bed to provide an effectivedemagnetization coefficient of from about 0.0027 to about 0.174, whichcomprises particles containing a non-ferromagnetic refractory, porousinorganic oxide component composited with a single elongatedferromagnetic component, the ferromagnetic component being multidomain,having dimensions of at least 1 μm in all directions and alength:diameter (L/D) ratio of at least 2 but not more than 17.3, saidferromagnetic component being present in the composite particles as aninclusion within a matrix formed by said nonferromagnetic component, andconstituting at least 0.5%, but not more than 3/2(L/D)² of the totalvolume of each particle, where L/D is the ratio of the longest dimensionof the ferromagnetic component relative to the shortest dimension, andthe particles can, in said magnetically stabilized fluidized bed rotate,or turn to line up the long dimension of a ferromagnetic componentparallel to the direction of the field and a short dimensionperpendicular to the direction of the field, wherein a catalyticallyeffective amount of a catalytically active metal is dispersed on thesurface of the composite particles, and the composite particles arecatalytically active.
 2. The composition of claim 1 wherein the volumeof the ferromagnetic component contained in the composite constitutes atleast 5 percent, but not more than 37.5 percent of the total volume ofeach particle.
 3. The composition of claim 2 wherein the length:diameterratio of the ferromagnetic component ranges no higher than about 5.5. 4.The composition of claim 1 wherein the length:diameter ratio of theferromagnetic component ranges no higher than about 5.5.
 5. Thecomposition of claim 1 wherein the demagnetization coefficient of amagnetically stabilized bed formed from the particles ranges from about0.022 to about 0.108.
 6. As a composition of matter, particulatematerial which can be oriented within, and formed into a magneticallystabilized fluidized bed to provide an effective demagnetizationcoefficient of from about 0.0027 to about 0.174, which comprisesparticles containing a non-ferromagnetic refractory, porous inorganicoxide component composited with a plurality of elongate ferromagneticcomponents, each ferromagnetic component being multidomain, havingdimensions of at least 1 μm in all directions, elongated in onedirection, and having a length:diameter (L/D) ratio of at least 2 butnot more than 19.5, said ferromagnetic components being present in thecomposite particles as inclusions within a matrix formed by saidnonferromagnetic component, and oriented in such a way that there is apreferred direction in each particle such that all the ferromagneticcomponents in said particle have a long dimension essentially parallelwith said preferred direction and constituting at least 0.5%, but notmore than 2π/3(L/D+1)², of the total volume of each particle, where L/Dis the average ratio of the longest dimension of the ferromagneticcomponents relative to the shortest dimension, and, in said magneticallystabilized fluidized bed, the particles can rotate, or turn to line upsaid preferred direction parallel to the direction of the field suchthat essentially all of the ferromagnetic components have a longdimension essentially parallel to the direction of the field, wherein acatalytically effective amount of a catalytically active metal isdispersed on the surface of the composite particles and the compositeparticles are catalytically active.
 7. The composition of claim 6wherein the volume of the ferromagnetic components contained in thecomposite constitute about 5 percent, but not more than 23.3 percent ofthe total volume of each particle.
 8. The composition of claim 6 whereinthe length:diameter ratio of the ferromagnetic components ranges nohigher than about 5.5.
 9. The composition of claim 6 wherein thedemagnetization coefficient ranges from about 0.022 to about 0.108.